THE CLYDE SEKIES OF SOILS. 9 



cases the local country rock. This resulted in the formation of wave- 

 cut terraces at the higher levels and in the deposition of sandy and 

 gravelly beaches and bars concentrically around the margins of the 

 lakes at different elevations corresponding to the different levels of 

 the receding glacial lake waters. 



The materials formed in the deltas of both glacial and upland 

 streams and the material deposited along the shore lines usually con- 

 stitute the coarser grained sediments of glacial lake deposition. It 

 is in such areas that large stone and coarse gravel are most frequently 

 encountered, while only smaller gravel and the different grades of 

 sand are found in the outwash plains and in those portions of the 

 stream deltas which were carried farthest into the lake areas. Else- 

 where the finer grained sediments, such as sandy loams, loams, and 

 clays, prevail. 



In the smaller glacial lake areas, particularly where lake occupa- 

 tion existed only for a brief period, the finer sediments dominate. 



In the case of all of the larger glacial lakes irregularities in the 

 surface of the glacial till, accentuated in some instances by the exist- 

 ence of local belts of moraine, gave rise to very unequal depth of 

 water within the lake area. In the case of the glacial Lakes Saginaw 

 and Maumee, curved moraines, concentric with the lake-shore line, 

 rose above the lake level at some period of the lake stage. The waters 

 of the lake acted against these moraines in the same manner as 

 against the upland till, forming beaches and distributing the coarser 

 and finer sediments along these shore lines and through the deeper 

 lake waters. Other portions of the till and of water-laid moraines 

 rose nearly to the surface of the lake and the crests of these sub- 

 merged ridges were subjected to a degree of wave action only less 

 than that along the shore lines. In certain areas the force of the 

 water was only sufficient to move and redistribute the finer grained 

 particles, while the larger gravel and the bowlders remained practi- 

 cally in their former position, being somewhat accumulated at the 

 surface through the removal of the finer earthy material. Where 

 such action has taken place unquestioned glacial lake deposits some- 

 times present the anomaly of abundant glacial bowlders and of large 

 cobblestones. In some instances it is even difficult to distinguish 

 between glacial moraine or till and the feebly reworked glacial sedi- 

 ments derived through the action of shallow lake waters across ridges 

 which rose nearly to the surface of the lake. 



In other instances the clrumlins and other glacial till ridges ex- 

 tended above the surface of the lake waters and only their sloping 

 flanks and the lower lands between them were covered by glacial 

 lake sediments. 



In every instance in the larger glacial lake basins the silt and 

 clay derived from the different sources outlined were deposited in 



55812°— Bull. 141—14 2 



